Document FR-A-2 437 954 describes an example of a seat of the type mentioned above.
In that seat, because the bottom of the seat back is subjected to relatively large front to back horizontal displacement during adjustment of the inclination of the seat back, it is necessary for the seat proper to follow those movements, otherwise a gap can be created between the rear of the seat proper and the bottom of the seat back when the seat back is inclined relatively little, and/or the bottom of the seat back can encroach on the seat proper when the seat back is inclined backwards to a greater extent.
That is why, in that known seat, the seat proper is secured to the seat back so as to pivot together with the seat back about its axis of rotation.
However, assembling the seat proper in that way is relatively unergonomic insofar as it gives rise to large variations in the inclination of the seat proper as a function of the inclination to which the seat back is adjusted. These variations in the inclination of the seat proper can be troublesome for the user of the seat, particularly if the user is the driver of the vehicle, since the driver must have easy access to the control pedals of the vehicle. In many cases, the driver of the vehicle must therefore readjust the longitudinal position of the seat as a whole after adjusting the inclination of the seat back, and that can become irksome.